Rising CO2 levels threaten aquatic life, studies show

Both marine and freshwater species are affected by acidifying water in ways that disrupt the entire food web, scientists warn

A shoal of fish off the coast of Queensland, Australia (Flickr/ robdownunder)

By
Tim Radford for Climate News Network

New studies warn that global warming is not good news for aquatic life, putting at risk the creatures both of the seas and of inland waterways.

Experiments in Australia confirm that increased temperatures driven by ever-rising atmospheric levels of the greenhouse gas carbon dioxide reduce the flow of energy up the marine food web, which would be bad news for the ocean’s top predators – and some prized fish catches.

They built 12 huge laboratory aquaria with water temperatures and acidity levels that matched predictions of climate change, and then introduced a range of sea creatures: algae, shrimp, sponges, snails, fishes and so on.

They found that the plants flourished, largely in the form of cyanobacteria, or blue-green algae. “This increased primary productivity does not support food webs, however, because these cyanobacteria are largely unpalatable, and they are not consumed by herbivores,” said Hadayet Ullah, who led the study.

“Healthy food webs are important for the maintenance of species diversity and provide a source of income and food for millions of people worldwide. Therefore, it is important to understand how climate change is altering marine food webs in the near future.”

Alarm, too, about the impact on freshwater species is not new. German biologists had access to data collected every month at four river dams from 1981 to 2015. They report in the journal Current Biology that acidification levels in the reservoirs had steadily increased in that time.

So they tested the response of species of daphnia, the water flea – and a source of food for other freshwater creatures – to changing water chemistry. The higher the acidity, the weaker the response of the water fleas to the scent of nearby predators.

“Many freshwater organisms rely on their sense of smell. If that sense is compromised in other species due to rising CO2 levels this development might have far-reaching consequences for the entire ecosystem,” said Linda Weiss of the Ruhr University of Bochum, who led the study.

“Follow-up studies must now be carried out, in order to determine if the acidification of freshwater systems is a global phenomenon and in what way other species react to rising CO2 levels.”